Polytetramethylene glycol is the industry standard for copolyester-ether soft segments. A wide variety of compositions ranging from hard plastics to tough elastomers to soft gums may be prepared depending upon the concentration and molecular weight of the polytetramethylene glycol soft segment.
U.S. Pat. No. 3,023,192 discloses other copolyester-ethers containing aromatic diesters residues, organic diol residues, and polyether glycol residues.
J. R. Wolfe, Jr. [Rubber Chemistry and Technology, Vol. 50, no. 4, (Sep./Oct. 1977)] teaches that titanate-ester-catalyzed melt condensation copolymerizations of polypropylene glycol having number average molecular weight of about 1000 with dimethyl terephthalate and 1,4-butanediol give copolyester-ethers having low inherent viscosities and poor properties as compared to copolyester-ethers prepared using polytetramethylene glycols of similar molecular weight. This is due largely to the high rate of thermal degradation of the polypropylene glycol at the polymerization temperatures (255.degree. C). Wolfe also teaches that the effect of having secondary hydroxyls rather than primary hydroxyls is minor as using ethylene oxide capped polypropylene glycols gives only marginal improvement in the inherent viscosity. The use of higher molecular weight polypropylene glycols, up to a number average molecular weight of about 2000, was found to give materials with greatly diminished properties due to the insolubility of the higher molecular weight species in the polymerization melt.
U.S. Pat. No. 5,466,759 discloses saturated polyether polyols having at least 98 percent primary terminal hydroxyl groups and comprising n repeat units of residue (1) and m repeat units of residue (2), wherein residues (1) and (2) have the structures: ##STR2## and m+n is in the range 2 to 70 and m/(n+m) is in the range 0.05 to 0.98. These polyether polyols are prepared by first polymerizing 3,4-epoxy-1-butene to produce unsaturated polyether precursors comprising residues (3) and (4) having the structures: ##STR3## and then hydrogenating the unsaturated polyether precursors.
A series of papers [L. P. Blanchard, et al., J. Polym. Sci., Part A-1, 9(12), 3547-54 (1971); L. P. Blanchard, et al., Kinet. Mech. Polyreactions, Int. Symp. Macromol. Chem., Prepr., Volume 1, 395-9. Akad. Kiado: Budapest, Hung. (1969); and J. M. Hammond, J. Polym. Sci., Part A-1, 9(2), 265-79 (1971)] teach that a mixture of cyclic oligomers and polyether glycols containing residue (1) and minor amounts of residue (2) can be prepared by the copolymerization of 1,2-butylene oxide and tetrahydrofuran in the presence of boron trifluoride etherate and a glycol initiator.